Canon 1.4x TC won't fit with the 70-300L, so it is not a choice for this combo. Folks will want to compare with the 100-400L, but the reason I got the 70-300L is it is a better, lighter, smaller lens than the 100-400 for a walk around and medium telephoto lens. I don't use the 1.4x much on it, but have done some test shots with hummingbirds and they look fine (even in not so ideal lighting).

Appreciate your confirmation, Lnguyen1203. I could never tell for sure, from what others all over the internet have said about this combo, until your definitive statement. I'll be ordering up one Kenko Teleplus PRO 300 DGX 1.4x AF Teleconverter. Thanks!

Appreciate your confirmation, Lnguyen1203. I could never tell for sure, from what others all over the internet have said about this combo, until your definitive statement. I'll be ordering up one Kenko Teleplus PRO 300 DGX 1.4x AF Teleconverter. Thanks!

You're welcome. Just remember to substrate about 1 stop of light. I don't quite understand how the Canon light meter works, but that is my experience. The 5D3 knows the presence of the Kenko and will give you the correct focal length and aperture setting, but the light metering is off by about 1 stop.

Can you tell us how much additional working distance the 1.4x adds to your 100L?

The tc converts the 100mm lens into a 140mm lens and still focuses to infinity (unlike extension tubes) - the working distance difference is significant for easily frightening critters (I'm (still) on crop, so it's actually 100x1.6x1.4). The iq of 100L+tc is excellent.

And will the 5D3/70-300L + 1.4x auto focus at f/8 with current firmware?

Yes, though there have been some reports with problems on the 5d3 (check these threads). Be sure to get the newestdgx with the blue dot, and from a big retailer so you get even the latest model from that (I suspect Kenko does silent firmware updates).

Appreciate your confirmation, Lnguyen1203. I could never tell for sure, from what others all over the internet have said about this combo, until your definitive statement. I'll be ordering up one Kenko Teleplus PRO 300 DGX 1.4x AF Teleconverter. Thanks!

I'm not sure if this completely true. I remember reading on TDP that the 1.4x can be mounted when the 70-300L is zoomed out a bit.

What I just discovered, however, is that the 70-300 L's rear element retracts into the lens far enough that, at about 250mm, there is enough clearance for the 1.4x to mount.

The available focal length range is about 350-420mm. There is a physical bump at the lower end of that range with (guessing) the rubber around the edge of the extender element contacting the rear 70-300 L lens element or its edge ring. This combination indeed autofocuses on the 1D X with the new firmware.

I'll put this combination on the ISO 12233 chart testing list to see what the image quality looks like, but ... I'm not sure that I recommend mounting this combination due to potential damage the to lens. I'll try to find out what Canon says about this.

TDP also has ISO crops of the 70-300L with 1.4x, where it is shown to be softer than the 100-400L

RandonOrbits, that applies to the Canon 1.4x, because of its design. The Kenko design is different, and allows it to be used over the entire 70-300L range. I don't have either tele-extender, so this isn't from personal experience, but that seems to be the consensus. And as for the extender eating another stop of light and impacting sharpness, I think that's the expected price you pay for gaining the reach.

You say that with the Kenko 1.4x the 5D3 autofocuses ... will this combo work with the 100-400 also as it will also result in a max aperture of f/8?

The Kenko tc tricks the camera into focusing @f8 while the Canon tc makes the camera do what its supposed to to - disable af @f8 to sell more 1d series cameras (or 5d3 sometime in 2013). The Kenko also works on *all* lenses, while the Canon is only designed for a small selection.

RandonOrbits, that applies to the Canon 1.4x, because of its design. The Kenko design is different, and allows it to be used over the entire 70-300L range. I don't have either tele-extender, so this isn't from personal experience, but that seems to be the consensus. And as for the extender eating another stop of light and impacting sharpness, I think that's the expected price you pay for gaining the reach.

RandonOrbits, that applies to the Canon 1.4x, because of its design. The Kenko design is different, and allows it to be used over the entire 70-300L range. I don't have either tele-extender, so this isn't from personal experience, but that seems to be the consensus. And as for the extender eating another stop of light and impacting sharpness, I think that's the expected price you pay for gaining the reach.

Yes, I agree. I'm saying that for those that already have a Canon extender, it'll work on the 70-300L on the long end and that you might not need to get extender specifically for the 70-300L.